This invention relates to unexpected discovery of surfactants which demonstrate improved surfactant recovery from aqueous solution upon ultrafiltration.
Because of environmental and economic concerns, it is important to remove and, desirably, recover for reuse active ingredients from aqueous by-product or waste solutions. Recovery and recycling not only reduces or eliminates the discharge of contaminated water into the environment but can also reduce the overall cost of industrial processes. This is of particular importance in processing aqueous solutions containing surfactants as they can be a costly component of the solution.
Ultrafiltration equipment can be used to overcome certain waste disposal problems in connection with aqueous solutions, whether using polymeric or sintered metal/sintered metal oxide filters. The economics of these processes in recovering surfactants have been seriously hampered since many of the conventional surfactants are not recovered in the permeate. The ability to recycle and reuse surfactants recovered from aqueous solutions can be significantly reduced thereby necessitating back addition of surfactant to bring the surfactant in solution to the original level. This is a significant problem in the area of recycling as full economics cannot be achieved.
Systems have been disclosed that claim significant recovery of water-based cleaning systems in the permeate upon ultrafiltration of waste though expressions of dissatisfaction have been heard concerning the filterability and recovery of existing water-based cleaning formulations. Whereas U.S. Pat. No. 5,205,937 to Bhave et. al. asserts to disclose aqueous cleaning systems wherein high percentages of the cleaner passes through the filter in the permeate for recycling, the amount of cleaner in the permeate is measured by HCI titration which is a measure of the caustic or sodium hydroxide present, not the surfactant. Most of the nonionic surfactants disclosed therein do not in fact pass through the membrane.
It is known that certain sultaine surfactants as disclosed in U.S. Pat. No. 4,891,159 provide effective surfactant properties in highly alkaline cleaning solutions making them useful in paint stripping compositions, hard surface cleaners, oven cleaners, wax strippers, degreasers, aluminum cleaners, bottle washing compositions and at lower alkalinity, laundry and dish washing detergents and hand cleansers. However, these surfactants are not taught to provide any significant benefits when used in connection with an ultrafiltration based surfactant separation and recovery system.
The present invention is directed to the finding that surfactant-containing aqueous compositions containing a certain group of amphoteric surfactants unexpectedly provide improved surfactant recovery in the permeate after ultrafiltration. More particularly, it is discovered that a certain class of betaine and amide oxide amphoteric surfactants provide superior surface activity in aqueous cleaner systems while at the same time pass through the filtration membranes for efficient recycling capabilities.